Researchers
led by a Washington State University biologist have found that arid areas,
among the biggest ecosystems on the planet, take up an unexpectedly large
amount of carbon as levels of carbon dioxide increase in the atmosphere. The
findings give scientists a better handle on the earth's carbon budget — how
much carbon remains in the atmosphere as CO2, contributing to global warming,
and how much gets stored in the land or ocean in other carbon-containing forms.

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"It
has pointed out the importance of these arid ecosystems," said R. Dave Evans, a
WSU professor of biological sciences specializing in ecology and global change.
"They are a major sink for atmospheric carbon dioxide, so as CO2 levels go up,
they’ll increase their uptake of CO2 from the atmosphere. They'll help take up
some of that excess CO2 going into the atmosphere. They can't take it all up,
but they'll help."

The
findings, published in the journal Nature Climate Change, come after a novel
10-year experiment in which researchers exposed plots in the Mojave Desert to
elevated carbon-dioxide levels similar to those expected in 2050. The
researchers then removed soil and plants down to a meter deep and measured how
much carbon was absorbed.

"We
just dug up the whole site and measured everything," said Evans.

The
idea for the experiment originated with scientists at Nevada's universities in
Reno and Las Vegas and the Desert Research Institute. Evans was brought in for
his expertise in nutrient cycling and deserts, while researchers at the
University of Idaho, Northern Arizona University, Arizona State University and
Colorado State University also contributed.

Funding
came from the U.S. Department of Energy's Terrestrial Carbon Processes Program
and the National Science Foundation's Ecosystem Studies Program.

Vast Lands play significant role.

The
work addresses one of the big unknowns of global warming: the degree to which
land-based ecosystems absorb or release carbon dioxide as it increases in the
atmosphere. Receiving less than 10 inches of rain a year, arid areas run in a
wide band at 30 degrees north and south latitude. Along with semi-arid areas,
which receive less than 20 inches of rain a year, they account for nearly half
the earth’s land surface.

Forest
soils have more organic matter and, square foot for square foot, hold much more
carbon. But because arid soils cover so much area, they can have an outsize
role in the earth's carbon budget and in how much the earth warms as
heat-trapping gases accumulate in the atmosphere.